Minimally invasive method and apparatus for placing facet screws and fusing adjacent vertebrae

ABSTRACT

The present invention provides a minimally invasive apparatus for placing screws across a facet joint between adjacent first and second vertebrae. The apparatus includes a first K-wire for inserting into the spinous process of the first vertebrae and a first fixation block removably connected to the first K-wire. The apparatus further includes a second K-wire for inserting into a transverse process of the second vertebrae and a second fixation block removably connected to the second K-wire. A rod member is removably connected to both of the first and second fixation blocks. A swivel block assembly includes relatively movable first and second block members. The rod member is removably connected to the first block member. A cannula extends from the second block member. The screws are insertable through the cannula for implantation across the facet joint. Methods for using the apparatus to place facet screws and fuse adjacent vertebrae are also provided.

TECHNICAL FIELD

The present invention relates to a minimally invasive method andapparatus for placing facet screws and fusing adjacent vertebrae.

BACKGROUND OF THE INVENTION

Over 200,000 spinal fixation and spinal fusion procedures are performedannually to correct various congenital and degenerative spinal disordersin humans. Many of these corrective surgical procedures are performed inthe lumbar and lumbosacral regions of the spine where traumatic andage-related disc degeneration is common. One such procedure involves theimplantation of spinal fixation instrumentation, including plates androds, using pedaled screws. Another procedure involves the implantationof one or more anterior fusion cages into the intervertebral disc spacefollowing a discectomy. These and other known spinal fixation and/orfusion procedures can be quite invasive, traumatic, and time consuming.Further, problems with post-operative stability and pseudoarthrosis areoften associated with many of these procedures.

It is well known that the two facet joints, which are formed betweeneach pair of adjacent vertebrae, share and support the axial load on thespine with a respective intervertebral disc. Accordingly, it has beensuggested to place screws either directly across the facet joints ofadjacent vertebrae or indirectly across the facet joints through thelamina (i.e. translaminar) as both a primary means for spinal fixationand as a secondary means for fixation to augment anterior fusion orpedicle screw fixation instrumentation. Indeed, this suggestion has beenaccepted by many surgeons as facet screws (direct and translaminar) arenow being implanted on a regular basis. In order to further improve uponthe use of such facet screws, a minimally invasive method and apparatusfor accurately and repeatably placing the facet screws for implantationacross the facet joints is needed.

SUMMARY OF THE INVENTION

The present invention is a minimally invasive apparatus for placingscrews across a facet joint between adjacent first and second vertebrae.The apparatus comprises a first K-wire for inserting into the spinousprocess of the first vertebrae and a first fixation block removablyconnected to the first K-wire. The apparatus further comprises a secondK-wire for inserting into a transverse process of the second vertebraeand a second fixation block removably connected to the second K-wire. Arod member is removably connected to both of the first and secondfixation blocks. A swivel block assembly comprises relatively movablefirst and second block members. The rod member is removably connected tothe first block member. A cannula extends from the second block member.The screws are insertable through the cannula for implantation acrossthe facet joint.

In accordance with one aspect of the invention, each of the first andsecond K-wires includes means for measuring axial length along theK-wires.

In accordance with another aspect of the invention, the rod memberincludes means for measuring axial length along the rod member.

In accordance with another aspect of the invention, the swivel blockassembly includes positioning means for controllably adjusting theangular position of the first and second block members relative to eachother.

The present invention further includes an apparatus for placingtranslaminar screws across a facet joint between adjacent first andsecond vertebrae in a minimally invasive surgical procedure. Theapparatus comprises a first K-wire for inserting into the spinousprocess of the first vertebrae and a second K-wire for inserting into atransverse process of the second vertebrae. The apparatus furtherincludes first and second fixation blocks having perpendicularlyextending first and second passages. The first K-wire extends into thefirst passage in the first fixation block and the second K-wireextending into the first passage in the second fixation block. A rodmember extends through the second passage in the first fixation blockand through the second passage in the second fixation block. A swivelblock assembly comprises relatively movable first and second blockmembers. The swivel block assembly includes a third passage extendingthrough the first block member and a fourth passage extending throughthe second block member. The rod member extends into the third passage.A cannula extends into the fourth passage in the second block member.The translaminar screws are insertable through the cannula forimplantation across a facet joint between the first and secondvertebrae.

In accordance with one aspect of the invention, the first and secondpassages in the first fixation block are offset from each other by apredetermined amount. In accordance with another aspect of theinvention, the first and second passages in the second fixation blockare offset from each other by the predetermined amount.

The present invention further provides a minimally invasive surgicalmethod for fusing adjacent upper and lower vertebrae. The methodutilizes an apparatus comprising first and second K-wires, first andsecond fixation blocks, a swivel block having relatively movable firstand second block members, a rod member extending between the fixationblocks and the first block member, and a cannula extending from thesecond block member. The first K-wire is inserted into the center of thespinous process of the upper vertebrae. The second K-wire is insertedinto a transverse process on a first side of the lower vertebrae. Thefirst fixation block is secured to the first K-wire and the secondfixation block is secured to the second K-wire with the rod memberextending across the K-wires. The second block member of the swivelblock assembly is secured relative to the first block member to achievea desired angle for a first axis along which a first screw will beimplanted into the facet joint on the first side. The swivel blockassembly is secured at a desired axial position on the rod member.Percutaneous access to the second side of the upper vertebrae along thefirst axis is then obtained via the cannula. A first screw is insertedthrough the cannula along the first axis and implanted across the facetjoint on the first side to attach the upper and lower vertebrae.

In accordance with additional aspects of the inventive method, thecannula is moved to aim the cannula toward the facet joint on the secondside of the vertebrae along a second axis. Percutaneous access along thesecond axis is then obtained to the facet joint on the second side viathe cannula and a bone graft material is placed into the facet joint onthe second side through the cannula to assist with fusion of the upperand lower vertebrae.

In accordance with a further aspect of the inventive method, a burringbit is inserted into the cannula and used to burr the articular surfacesof the facet joint on the second side to widen the facet joint foraccepting the bone graft material.

In accordance with still other aspects of the inventive method, thecannula is removed from percutaneous insertion and the second K-wire isremoved from the transverse process on the first side of the lowervertebrae. The second K-wire is then inserted into the transverseprocess on the second side of the lower vertebrae. The second fixationblock is then secured to the second K-wire. Next, the first fixationblock is released from the first K-wire and is rotated with the rodmember extending across the K-wires. The first fixation block is securedto the first K-wire. The second block member of the swivel blockassembly is then secured relative to the first block member to achieve adesired angle for a third axis along which a second screw will beimplanted into the facet joint on the second side. The swivel blockassembly is secured at a desired axial position along the rod member.Percutaneous access to the first side of the upper vertebrae is obtainedvia the cannula. A second screw is inserted through the cannula andimplanted along the third axis across the facet joint on the second sideto attach the upper and lower vertebrae.

In accordance with additional aspects of the inventive method, thecannula is moved to aim the cannula along a fourth axis toward the facetjoint on the first side previously secured with the first screw.Percutaneous access to the facet joint on the first side is obtained viathe cannula and a bone graft material is placed through the cannula intothe facet joint around the previously implanted first screw to assistwith fusion of the upper and lower vertebrae.

The present invention also provides a minimally invasive surgical methodfor placing screws through the lamina and across the facet jointsbetween adjacent upper and lower vertebrae. The inventive methodutilizes an apparatus comprising first and second K-wires, first andsecond fixation blocks, a swivel block having relatively movable firstand second block members, a rod member extending between the fixationblocks and the first block member, and a cannula extending from thesecond block member. The first K-wire is inserted into the center of thespinous process of the upper vertebrae. The second K-wire is insertedinto a transverse process on a first side of the lower vertebrae so thatthe second K-wire is parallel to the first K-wire in both the sagittaland coronal planes. The first fixation block is secured to the firstK-wire and the second fixation block to the second K-wire with the rodmember extending across the K-wires. A desired axial position iscalculated for the swivel block assembly along the rod member. A desiredangle for the centerline of the cannula is calculated to extend from asecond side of the vertebrae toward the facet joint on the first sidealong a first axis. The second block member of the swivel block assemblyis secured relative to the first block member to achieve the desiredangle for the first axis. The swivel block assembly is secured at thedesired axial position along the rod member. Percutaneous access to thejunction of the lumina and the spinous process on the second side of theupper vertebrae is then obtained via the cannula. A first screw isinserted through the cannula. The first screw is implanted along thefirst axis across the facet joint on the first side to attach the upperand lower vertebrae.

In accordance with additional aspects of the inventive method, thecannula is removed from percutaneous insertion on the second side andthe second K-wire is removed from the transverse process on first sideof the lower vertebrae. The second K-wire is then re-inserted into thetransverse process on the second side of the lower vertebrae so that thesecond K-wire is again parallel to the first K-wire in both the sagittaland coronal planes. The second fixation block is secured to the secondK-wire. The first fixation block is released from the first K-wire andis rotated with the rod member extending across the K-wires. The firstfixation block is then secured to the first K-wire. A desired axialposition is calculated for the swivel block assembly along the rodmember and the swivel block assembly is secured at the desired axialposition. A desired angle is calculated for the centerline of thecannula to extend from the first side of the vertebrae toward the facetjoint on the second side along a third axis. The second block member ofthe swivel block assembly is then secured relative to the first blockmember to achieve the desired angle. Percutaneous access to the junctionof the lamina and the spinous process on the first side of the uppervertebrae is obtained via the cannula and a second screw is insertedinto the cannula. The second screw is implanted along the third axisacross the facet joint on the second side to attach the upper and lowervertebrae.

In accordance with further aspects of the inventive method, the cannulais moved from its position over the lamina on the first side of theupper vertebrae and the first and second block members are released toallow relative movement. The second block member is swiveled to aim thecenterline of the cannula along a fourth axis toward the facet joint onthe first side previously secured with the first screw. Percutaneousaccess to the facet joint on the first side is obtained via the cannulaand a bone graft material is placed through the cannula into the facetjoint on the first side around the previously implanted first screw toassist with fusion of the upper and lower vertebrae.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view of an apparatus for placing facet screws inaccordance with the present invention;

FIG. 2 is a perspective view of a component of the apparatus of FIG. 1;

FIG. 2A is a perspective view of a component of the apparatus of FIG. 1;

FIG. 3 is a perspective view of another component of the apparatus ofFIG. 1;

FIG. 4 is a perspective view of another component of the apparatus ofFIG. 1;

FIG. 4A is a perspective view of another component of the apparatus ofFIG. 1;

FIG. 5 is an exploded perspective view of another component of theapparatus of FIG. 1;

FIG. 6 is a perspective view of a screw to be implanted in accordancewith the present invention;

FIG. 7 is a schematic view of adjacent lumbar vertebrae in thetransverse plane and illustrating components of the apparatus of FIG. 1at an early stage of the inventive method for placing a facet screwacross a facet joint;

FIG. 8 is a schematic posterior view of the apparatus at a subsequentstage to that of FIG. 7;

FIG. 9 is a schematic side view of FIG. 8;

FIGS. 10-12 are views similar to FIG. 7 illustrating various stepsaccording to the inventive method;

FIG. 13 is a schematic posterior view of the apparatus;

FIGS. 14 and 15 are views similar to FIG. 12 illustrating additionalsteps according to the inventive method;

FIG. 16 is a view similar to FIG. 15 illustrating components of theapparatus of FIG. 1 in different positions for placing a facet screwacross a facet joint on the opposite side;

FIG. 17 is a schematic posterior view of the apparatus at a subsequentstage to that of FIG. 16;

FIG. 18 is a schematic side view of the opposite side shown in FIG. 17;

FIGS. 19-21 are views similar to FIG. 16 illustrating various stepsaccording to the inventive method;

FIG. 22 is a schematic posterior view of the apparatus;

FIGS. 23 and 24 are views similar to FIG. 21 illustrating additionalsteps; and

FIG. 25 is a view similar to FIG. 24 illustrating the facet screwsimplanted across the facet joints in the adjacent vertebrae.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a minimally invasive method andapparatus for placing facet screws and fusing adjacent vertebrae. Asrepresentative of the present invention, FIG. 1 illustrates an apparatus10 comprising first and second Kirschner wires 12 and 14 (commonlyreferred to as “K-wires”), first and second fixation blocks 16 and 18, arod member 20, a swivel block assembly 22 comprising first and secondblock members 24 and 26, and a cannula 28.

As may be seen in FIG. 3, the rod member 20 is a cylindrical componentthat may be hollow or solid and is made from any suitable metal orplastic. The rod member 20 has oppositely disposed first and second ends30 and 32 and an outer diameter of 4 to 7 mm. The rod member 20 includesan outer surface 34 with graduations for measuring axial distances alongits length. It is contemplated that other means for measuring axiallength along the rod member 20 could also be used.

The first and second K-wires 12 and 14 (FIG. 2) are identical parts,although it should be understood that the K-wires could have differentsizes or shapes. Each of the first and second K-wires 12 and 14 is anelongate rod made of a biocompatible metal or other suitable materialwith an outer diameter of 2 to 4 mm. As shown in FIGS. 2 and 2A, eachK-wire 12 and 14 has oppositely disposed distal and proximal ends 40 and42 and a cylindrical outer surface 44 extending between the ends. Thedistal end 40 of each of the K-wires 12 and 14 includes self-tappingthreads 46. The cylindrical outer surface 44 of each of the K-wires 12and 14 includes graduations for measuring axial lengths along eachK-wire. It is contemplated that other means for measuring axial lengthalong the K-wires 12 and 14 could also be used.

The first and second fixation blocks 16 and 18 (FIGS. 4 and 4A) are alsoidentical components, although it should be understood that certainaspects of the fixation blocks need not be identical. Each of the firstand second fixation blocks 16 and 18 is a generally rectangular partmade of any suitable metal or plastic. The first fixation block 16 (FIG.4) includes perpendicularly extending first and second passages 50 and52. As shown in FIG. 3, the first and second passages 50 and 52 areoffset from each other by a predetermined amount and thus do notintersect. In the assembled condition of FIG. 1, the first K-wire 12extends into the first passage 50 in the first fixation block 16 and therod member 20 extends into the second passage 52.

The first fixation block 16 further includes threaded fasteners in theform of thumbscrews 54 that extend into the first and second passages 50and 52 for securing the first K-wire 12 and the rod member 20 in thefirst and second passages, respectively. It should be understood,however, that other suitable means for securing the first K-wire 12 andthe rod member 20 to the first fixation block 16, such as clamps,latches, ratchet mechanisms, etc., could also be used, and that thesecuring means could be positioned on the exterior of the first fixationblock.

In an identical fashion to the first fixation block 16, the secondfixation block 18 includes perpendicularly extending first and secondpassages 56 and 58 that are offset from each other by a predeterminedamount and thus do not intersect. The predetermined amount of offsetbetween the first and second passages 56 and 58 in the second fixationblock 18 is the same as the predetermined amount of offset between thefirst and second passages 50 and 52 in the first fixation block 16. Inthe assembled condition of FIG. 1, the second K-wire 14 extends into thefirst passage 56 in the second fixation block 18 and the rod member 20extends into the second passage 58.

The second fixation block 18 further includes threaded fasteners in theform of thumbscrews 54 that extend into the first and second passages 56and 58 for securing the second K-wire 14 and the rod member 20 in thefirst and second passages 56 and 58, respectively. It should beunderstood, however, that other suitable means for securing the secondK-wire 14 and the rod member 20 to the second fixation block 18, such asclamps, latches, ratchet mechanisms, etc., could also be used, and thatthe securing means could be positioned on the exterior of the secondfixation block.

As shown in FIG. 4, the first and second block members 24 and 26 of theswivel block assembly 22 are movable relative to each other about anaxis 60. Each of the first and second block members 24 and 26 is agenerally rectangular part made of any suitable metal or plastic. Thefirst block member 24 includes a passage 62 for receiving the rod member20. A threaded fastener in the form of a thumbscrew 54 extends into thepassage 62 for securing the rod member 20 in the passage. The secondblock member 26 further includes a passage 64 for receiving the cannula28. A threaded fastener in the form of a thumbscrew 54 extends into thepassage 64 for securing the cannula 28 in the passage. It should beunderstood, however, that other suitable means for securing the rodmember 20 and the cannula 28 to the swivel block assembly 22, such asclamps, latches, ratchet mechanisms, etc., could also be used, and thatthese securing means could be positioned on the exterior of the swivelblock assembly.

The first and second block members 24 and 26 further include abuttingsurfaces 66 and 68, respectively, with means for controllably adjustingthe angular position of the block members relative to each other. Inaccordance with the illustrated embodiment of the invention, this isaccomplished via a first ring of radially extending serrations 70 on thesurface 66 of the first block member 24 that is centered on the axis 60and engaged with a second ring of radially extending serrations 72 onthe surface 68 of the second block member 26 that is also centered onthe axis 60. A threaded fastener in the form of a thumbscrew 74 extendsthrough the first block member 24 and into a threaded opening 76 in thesecond block member 26 along the axis 60 for securing the block membersin a desired relative angular position. It should be understood,however, that other suitable means for securing the block members 24 and26 in a desired angular position could be used, and that the securingmeans could be located elsewhere on the block members. Further, itshould also be understood that other suitable means for controllablyadjusting the relative angular position of the first and second blockmembers 24 and 26 could be employed.

The cannula 28 (FIG. 1) is a thin-walled hollow cylinder made of abiocompatible metal or other suitable material and has oppositelydisposed distal and proximal ends 80 and 82. In accordance with oneembodiment of the present invention, the cannula 28 has an outerdiameter of about 4.5 mm and an inner diameter of about 4.3 mm, althoughit should be understood that these dimensions may be varied between 4and 6 mm for the outer diameter and 3.5 to 5 mm for the inner diameter.

FIG. 6 illustrates a screw 84 to be implanted in accordance with thepresent invention. The screw 84 is a self-tapping facet screw made of abiocompatible material, such as titanium. As illustrated in FIG. 6, thescrew 84 has a head 86 with a triangular-shaped receptacle 88. Inaccordance with one embodiment, the screw has a major diameter of 4.3 mmand a minor diameter of 3.8 mm, but it should be understood that thesedimensions can be varied based on the pathology and surgical needs. Thelength L of the screw 84 is determined during surgery as discussedbelow.

To use the apparatus 10 to place the facet screw 84 across a first facetjoint 100 between adjacent vertebrae, such as the L4 and L5 vertebraeshown in FIGS. 7-9, in a minimally invasive procedure, the patient isplaced in the prone position and X-ray imaging equipment is set-up toprovide views in both the antero-posterior (AP) plane and the lateralplane so that the procedure can be performed under fluoroscopicguidance. It should be understood to those skilled in the art that otherknown navigation assistance devices and equipment could alternatively beused. A stab incision is then made through the skin and the first K-wire12 is inserted through the incision and into the center of the spinousprocess of the L4 vertebrae. As may be seen in FIGS. 7 and 9, the distalend 40 of the first K-wire 12 is screwed into the spinous process untilthe distal tip reaches a point along a first axis 102 on which a firstscrew 84 is to be inserted.

Next, through another percutaneous stab incision, the second K-wire 14is inserted into the transverse process on a first side 104 (the leftside as viewed in FIG. 7) of the L5 vertebrae and extends in parallelwith the first K-wire 12 in both the sagittal and coronal planes asshown in FIGS. 7-9. The distal end 40 of the second K-wire 12 is screwedinto the transverse process just lateral to the facet joint 100 on thefirst side 104 of the vertebrae up to the junction of the transverseprocess and the pedicle on the first side.

The first fixation block 16 is then slid onto the first K-wire 12 withthe first K-wire extending into the first passage 50 in the firstfixation block. Similarly, the second fixation block 18 is slid onto thesecond K-wire 14 with the second K-wire extending into the first passage56 in the second fixation block. The first end 30 of the rod member 20is slid then into the second passages 52 and 58 in the first and secondfixation blocks 16 and 18, respectively, so that it extends across thefirst and second K-wires 12 and 14. The thumbscrews 54 that extend intothe second passages 52 and 58 are tightened to secure the rod member 20to the fixation blocks 16 and 18.

According to the inventive method, the next steps involve calculationsto determine the following three parameters: (1) the length L₁ of thescrew 84 to be implanted; (2) the desired angle A₁ for the cannula 28 toextend from the swivel block assembly 22, which provides the trajectoryfor the implantation of a first screw 84 across the facet joint 100 onthe first side 104; and (3) the desired axial position D₁ for the swivelblock assembly 22 along the rod member 20. As will be seen in thecalculations set forth below, the apparatus 10 according to the presentinvention utilizes the position and relationship of the first and secondK-wires 12 and 14 to determine the entry point and trajectory upon whichthe screw 84 is implanted into the L4 and L5 vertebrae.

The screw length L₁ is determined by measuring the axial difference X₁between the two identical K-wires 12 and 14 and measuring the horizontaldifference Y₁ between the two K-wires. The graduations on the K-wires 12and 14 and/or another suitable means can assist in taking thesemeasurements. The screw length L₁ is calculated with the followingequation: L₁=√(X₁ ²+Y₁ ²). Use of this equation to determine the desiredscrew length L₁ helps to ensure that the screw 84, when implanted acrossthe facet joint 100, will not extend beyond the cortex of the superiorarticular process where nerve damage could become an issue.

The desired angle A₁ for the cannula 28 to extend from the swivel blockassembly 22, which provides the trajectory for the implantation of thefirst screw 84 across the facet joint 100 on the first side 104, iscalculated based on the measured X and Y values and the angle betweenthese distances using the following equation: A₁=tan⁻¹ (Y₁/X₁). As shownin FIG. 5, the calculated angle A₁ between the proximal ends 42 of theK-wires 12 and 14 also defines the angle (A₁) between the centerline ofthe rod member 20 and the centerline 108 of the second passage 64through the second block member 26. The centerline 106 of the passage 64is also the centerline of the cannula 28 and is co-linear with the screwtrajectory axis 102, as may be seen in FIG. 7. The second block member26 is then rotated about the axis 60 relative to the first block member24 to set the desired angle A₁ for the centerline 106 of the cannula 28,which extends from the second block member. At the desired angle A₁, thefirst and second rings of serrations 70 and 72 on the first and secondblock members 24 and 26, respectively, are brought into engagement andsecured by the thumbscrew 74 to ensure that the relative angularposition of the block members is fixed. It should be understood by thoseskilled in the art that other means, such as an angle measuring device,for determining the desired angle A₁ could also be used in conjunctionwith the distances X₁ and Y₁, between the K-wires 12 and 14.

The axial position, or distance, D₁ for the swivel block assembly 22 onthe rod member 20 is calculated by first measuring the distance Z₁ ofpenetration of the first K-wire 12 (i.e., the distance Z₁ extendsbetween the distal tip of the first K-wire and the skin 108) using thegraduations on the first K-wire. The distance D₁, is then calculatedwith the following equation: D₁=(X₁/Y₁) Z₁. The distance D₁, for theswivel block assembly 22 along the rod member 20 is measured from thecenterline of the first K-wire 12 to the axis 60 of the swivel blockassembly. The graduations on the rod member 20 or another suitable meanscan be used for setting the swivel block assembly 22 at the desiredaxial position.

Next, the swivel block assembly 22 is slid onto the second end 32 of therod member 20, which is projecting out over a second side 110 (or rightside as viewed in FIG. 7) of the L4 and L5 vertebrae, with the rodmember 20 extending through the passage 62 in the first block member 24.The thumbscrew 54 is used to secure the swivel block assembly 22 at thecalculated desired axial position D₁ on the rod member 20.

The rod member 20 and the swivel block assembly 22 are then lowered to aheight above the skin 108 that provides sufficient clearance for theswivel block assembly as shown in FIG. 7. Finally, the first and secondfixation blocks 16 and 18 are secured to the first and the secondK-wires 12 and 14, respectively, with the thumbscrews 54. The apparatus10 is now in position for the first screw 84 to be placed across thefacet joint 100 on the first side 104 of the L4 and L5 vertebrae.

A scalpel (not shown) is used to incise the skin 108 on the second side110 of the vertebrae to accept the cannula 28. With the cannula 28temporarily removed, the incision is made using the passage 64 throughthe second block member 24 of the swivel block assembly 22 to orient theincision along the proper axes 102 and 106. Under fluoroscopic guidance,a guidewire 120 is passed through the incision along the axes 102 and106 to the starting point for the screw 84 which is located adjacent thejunction of the spinous process and the lamina as shown in FIG. 7. It iscontemplated that a Jamshidi needle or other suitable instrument couldbe used in place of the guidewire 120.

Next, a blunt obturator 122 is passed over the guidewire 120 to createsubcutaneous space for the cannula 28 along the axis 102. The cannula28, which is guided for movement along the axes 102 and 106 by virtue ofthe passage 64 through the second block member 26, is then passed overthe obturator 122 and the guidewire 120. The cannula 28 is moved alongthe axes 102 and 106 until the distal end of the cannula docks againstthe lamina on the second side 110 of the L4 vertebrae as shown in FIGS.8 and 9. The guidewire 120 and the obturator 122 are then removed fromthe cannula 28. At this point in the procedure, a small (e.g., 2 mm)diameter scope may be passed down the cannula 28 to inspect the anatomyand the condition of the vertebrae.

After ensuring that all of the thumbscrews 54 and 74 are secure and thatthe alignment of the axis 102 is correct, a drill bit 130 (FIG. 10) isinserted into the cannula 28. The drill bit 130 is rotated by a drill(not shown) to drill a pilot hole 132 along the axis 102 through thelamina on the second side 110 of the L4 vertebrae, through the inferiorarticular process on the first side 104 of the L4 vertebrae, across thefacet joint 100 on the first side, and into the superior articularprocess of the L5 vertebrae. It is contemplated that a drill guide (notshown) could be used to center the drill bit 130 in the cannula 28 andensure that the pilot hole 132 extends along the axis 102.

As shown in FIG. 11, the self-tapping screw 84 is then inserted into thecannula 28 and screwed into the pilot hole 132 using a driver 134. Inthe illustrated embodiment, the head 86 of the screw 84 has a maximumouter diameter that matches the inner diameter of a second cannula 136that is inserted into the cannula 28 to aid in keeping the screw alignedon the axis 102 during implantation. Further, the illustrated driver 134has a triangular tip for receipt in the receptacle 88 of the screw 84,although it should be understood that the receptacle and thecorresponding driver tip could utilize a different geometry. The screw84 is advanced until the head 86 seats against the lamina on the secondside 110 of the L4 vertebrae. Fluoroscopic guidance coupled with theaforementioned calculation to select the length L₁ of the screw 84ensures that the distal tip of the screw does not penetrate beyond thecortex of the L5 vertebrae. As implanted, the screw 84 extends acrossthe facet joint 100 to connect the inferior articular process of the L4vertebrae to the superior articular process of the L5 vertebrae.

With the first screw 84 implanted, the cannula 28 is removed from theskin 108 and the thumbscrew 74 is released to allow relative movement ofthe first and second block members 24 and 26. The second block member 26is then swiveled to aim the centerline 106 of the cannula 28 along asecond axis 140 (FIG. 13) that extends toward a facet joint 142 (FIG.12) on the second side 110 of the vertebrae. In order to aim the cannula28 toward the facet joint 142, the other thumbscrews 54 may also bereleased to allow additional movement of the swivel block assembly 22.Releasing the other thumbscrews 22 may allow the cannula 28 to bepositioned over the existing incision through the skin 108 while beingaimed toward the facet joint 142 along the axis 140 so that the sameincision can be utilized again.

After tightening all of the thumbscrews 54 and 74 to secure thecomponents of the apparatus 10 in the positions shown in FIG. 12, theguidewire 120 (or Jamshidi needle, etc.) is passed through the incisionalong the axis 140 to the surface of the facet joint 142 on the secondside 110 of the L4 and L5 vertebrae under fluoroscopic guidance. Next,the blunt obturator 122 is passed over the guidewire 120 to createsubcutaneous space for the cannula 28 along the axis 140. The cannula28, which is guided for movement along the axes 140 and 106 by virtue ofthe passage 64 through the second block member 26, is then passed overthe obturator 122 and the guidewire 120. The cannula 28 is moved alongthe axes 140 and 106 until the distal end of the cannula 28 docksagainst the surface of the facet joint 142 as shown in FIGS. 13 and 14.The guidewire 120 and the obturator 122 are then removed from thecannula 28.

After ensuring that all of the thumbscrews 54 and 74 are secure and thatthe alignment of the axis 140 is correct, a burring bit 150 (FIG. 14) isinserted into the cannula. The burring bit 150 is rotated by a drill(not shown) to burr the opposing surfaces 152 and 154 of the inferiorarticular process and the superior articular process on the second side110 of the L4 and L5 vertebrae, respectively. Burring these surfaces 152and 154 widens the facet joint so that a bone graft material is moreeasily placed into the facet joint 142. It is contemplated that thecannula 28 may be moved slightly along the facet joint 142 during theburring process in order to access a larger area of the facet joint withthe burring bit 150.

After the articular surfaces 152 and 154 of the facet joint 142 on thesecond side 110 of the L4 and L5 vertebrae have been burred out, a bonegraft (or bone substitute) material 160 (FIG. 15) for helping to fusethe L4 and L5 vertebrae is placed into the facet joint 142 through thecannula 28. The bone graft material 160 may be fed into the facet joint142 using any known suitable instrument(s). The cannula 28 is thenremoved from the incision on the second side 110 of the vertebrae.

The next steps in the process are to loosen all of the thumbscrews 54and 74, remove the fixation blocks 16 and 18 from the K-wires 12 and 14,and disassemble the swivel block assembly 22 from the rod member 20. Thesecond K-wire 14 is then removed from the transverse process on thefirst side 104 of the L5 vertebrae. Next, through another percutaneousstab incision, the second K-wire 14 is inserted into the transverseprocess on the second side 110 of the L5 vertebrae so that it againextends in parallel with the first K-wire 12 in both the sagittal andcoronal planes as shown in FIGS. 16-18. The distal end 40 of the secondK-wire 14 is screwed into the transverse process just lateral to thefacet joint 142 on the second side 110 of the vertebrae up to thejunction of the transverse process and the pedicle.

The first fixation block 16 is then slid onto the first K-wire 12 withthe first K-wire extending into the first passage 50 in the firstfixation block. Similarly, the second fixation block 18 is slid onto thesecond K-wire 14 with the second K-wire extending into the first passage56 in the second fixation block. The first end 30 of the rod member 20is slid then into the second passages 52 and 58 in the first and secondfixation blocks 16 and 18, respectively, so that it extends across thefirst and second K-wires 12 and 14. The thumbscrews 54 that extend intothe second passages 52 and 58 are tightened to secure the rod member 20to the fixation blocks 16 and 18.

Once again, the next steps in the process involve calculations todetermine the following three parameters: (1) the length L₂ of a secondscrew 84 to be implanted; (2) the desired angle A₂ for the cannula 28 toextend from the swivel block assembly, which provides a trajectory axis162 for the implantation of the second screw 84 across the facet joint142 on the second side 110; and (3) the desired axial position D₂ forthe swivel block assembly 22 along the rod member 20. As mentionedabove, the apparatus 10 according to the present invention utilizes theposition and relationship of the first and second K-wires 12 and 14 todetermine the entry point and trajectory upon which the second screw 84is implanted into the L4 and L5 vertebrae.

The screw length L₂ is determined by measuring the axial difference X₂between the two identical K-wires 12 and 14 and measuring the horizontaldifference Y₂ between the two K-wires. The graduations on the K-wires 12and 14 or another suitable means can assist in taking thesemeasurements. The screw length L₂is then calculated with the followingequation: L₂=√(X₂ ²+Y₂ ²). Use of this equation to determine the desiredscrew length L₂ helps to ensure that the second screw 84, when implantedacross the facet joint 142, will not extend beyond the cortex of thesuperior articular process where nerve damage could become an issue. Itshould be noted that in many cases, the lengths for the first and secondscrews 84 will likely be the same.

The desired angle A₂ for the cannula 28 to extend from the swivel blockassembly 22, which provides the trajectory for the implantation of thesecond screw 84 across the facet joint 142 on the second side 110, iscalculated with the following equation: A₂=tan⁻¹ (Y₂/X₂). As shown inFIG. 16, the calculated desired angle A₂ between the proximal ends 42 ofthe K-wires 12 and 14 also defines the angle (A₂) between the centerlineof the rod member 20 and the centerline 106 of the second passage 64through the second block member 26. The centerline of the passage 64 isalso the centerline of the cannula 162, as may be seen in FIG. 16. Thesecond block member 26 is then rotated about the axis 60 relative to thefirst block member 24 to set the desired angle A₂ for the centerline 106of the cannula 28, which extends from the second block member. At thedesired angle A₂, the first and second rings of serrations 70 and 72 onthe first and second block members 24 and 26, respectively are broughtinto engagement and secured by the thumbscrew 74 to ensure that therelative angular position of the block members is fixed. It should beunderstood by those skilled in the art that other means, such as anangle measuring device, for determining the desired angle A₂ could alsobe used in conjunction with the distances X₂ and Y₂ between the K-wires12 and 14.

The axial position, or distance, D₂ for the swivel block assembly 22 onthe rod member 20 is calculated by first measuring the distance Z₂ ofpenetration of the first K-wire 12 (i.e., the distance Z₂ extendsbetween the distal tip of the first K-wire and the skin 108) using thegraduations on the first K-wire. The distance D₂ is then calculated withthe following equation: D₂=(X₂/Y₂) Z₂. The distance D₂ for the swivelblock assembly 22 along the rod member 20 is measured from thecenterline of the first K-wire 12 to the axis 60 of the swivel blockassembly 22. The graduations on the rod member 20 or another suitablemeans can be used for setting the swivel block assembly 22 at thedesired axial position.

Next, the swivel block assembly 22 is then slid onto the second end 32of the rod member 20, which is projecting out over the first side 104 ofthe vertebrae, with the rod member extending through the passage 62 inthe first block member 24. The thumbscrew 54 is used to secure theswivel block assembly 22 at the calculated desired axial position D₂ onthe rod member 20.

The rod member 20 and the swivel block assembly 22 are then lowered to aheight above the skin 108 that provides sufficient clearance for theswivel block assembly as shown in FIG. 16. Finally, the first and secondfixation blocks 16 and 18 are secured to the first and second K-wires 12and 14, respectively, with the thumbscrews. The apparatus 10 is now inposition for the second screw 84 to be placed across the facet joint 142on the second side 110 of the vertebrae. It is important to note at thispoint that the predetermined offset between the first and secondpassages 50 and 52 in the first fixation blocks 16 and the first andsecond passages 56 and 58 in the second fixation block 18 positions therod member 20 and the swivel block assembly 22 so that the axis 162 forimplantation of the second screw 84 is offset from the axis 102 on whichthe first screw 84 was implanted. This offset ensures that the secondscrew 84 does not intersect with the first screw 84 as it extendsthrough the spinous process of the L4 vertebrae.

The scalpel (not shown) is used to incise the skin 108 on the first side104 of the vertebrae to accept the cannula 28. With the cannula 28temporarily removed, the incision is made using the passage 64 throughthe second block member 24 of the swivel block assembly 22 to orient theincision on the axes 106 and 162. Under fluoroscopic guidance, theguidewire 120 is passed through the incision along the axes 106 and 162to the starting point for the screw 84 which is located adjacent thejunction of the spinous process and the lamina as shown in FIG. 16. Asdiscussed above, it is contemplated that a Jamshidi needle or othersuitable instrument could be used in place of the guidewire 120.

Next, the blunt obturator 122 is passed over the guidewire 120 to createsubcutaneous space for the cannula 28 along the axis 162. The cannula28, which is guided for movement along the axes 106 and 162 by virtue ofthe passage 64 through the second block member 26, is then passed overthe obturator 122 and the guidewire 120. The cannula 28 is moved alongthe axes 106 and 162 until the distal end of the cannula docks againstthe lamina on the first side 104 of the L4 vertebrae as shown in FIGS.17 and 18. The guidewire 120 and the obturator 122 are then removed fromthe cannula 28. At this point in the procedure, the small diameter scopemay again be passed down the cannula 28 to inspect the anatomy and thecondition of the vertebrae.

After ensuring that all of the thumbscrews 54 and 74 are secure and thatthe alignment of the axis 162 is correct, the drill bit (FIG. 19) isinserted into the cannula 28. The drill bit 130 is rotated by a drill(not shown) to drill a pilot hole 132 along the axis 162 through thelamina on the first side 104 of the L4 vertebrae, through the inferiorarticular process on the second side 110 of the L4 vertebrae, across thefacet joint 142 and the bone graft material 160 therein, and into thesuperior articular process of the L5 vertebrae. It is contemplated thata drill guide (not shown) could be used to center the drill bit 130 inthe cannula 28 and ensure that the pilot hole 132 extends along the axis162.

As shown in FIG. 20, the self-tapping second screw 84 is then insertedinto the cannula 28 and screwed into the pilot hole 132 using the driver134. In the illustrated embodiment, the head 86 of the screw 84 has amaximum outer diameter that matches the inner diameter of the secondcannula 136 to aid in keeping the screw aligned on the axis 162 duringimplantation. Further, the illustrated screw head 86 has a triangularreceptacle for receiving the triangular tip on the driver 134, althoughit should be understood that the receptacle and the corresponding drivertip could utilize a different geometry. The screw 84 is advanced untilthe head 86 seats against the lamina on the first side 104 of the L4vertebrae. Fluoroscopic guidance coupled with the aforementionedcalculation to select the length L₂ of the screw ensures that the distaltip of the screw does not penetrate beyond the cortex of the L5vertebrae. As implanted, the second screw 84 extends across the facetjoint 142 and the bone graft material 160 in the facet joint connect theinferior articular process of the L4 vertebrae to the superior articularprocess of the L5 vertebrae.

With the second screw 84 implanted, the cannula 28 is removed from theskin 108 and the thumbscrew 74 is released to allow relative movement ofthe first and second block members 24 and 26. The second block member 26is then swiveled to aim the centerline 106 of the cannula 28 along afourth axis 170 (FIG. 22) that extends toward the facet joint 100 on thefirst side 104 of the vertebrae. In order to aim the cannula 28 towardthe facet joint 100, the other thumbscrews 54 may also be released toallow additional movement of the swivel block assembly 22. Releasing theother thumbscrews 54 may allow the cannula to be positioned over theexisting incision while being aimed toward the facet joint 100 along theaxis 170 so that the same incision can be utilized again.

After tightening all of the thumbscrews 54 and 74 to secure thecomponents of the apparatus 10 in the positions shown in FIG. 21, theguidewire 120 (or Jamshidi needle, etc.) is passed through the incisionalong the axis 170 to the surface of the facet joint 100 on the firstside 104 of the vertebrae under fluoroscopic guidance. Next, the bluntobturator 122 is passed over the guidewire 120 to create subcutaneousspace for the cannula 28 along the axis 170. The cannula 28, which isguided for movement along the axes 106 and 170 by virtue of the passage64 through the second block member 26, is then passed over the obturator122 and the guidewire 120. The cannula 28 is moved along the axes 106and 170 until the distal end of the cannula docks against the surface ofthe facet joint 100 as shown in FIGS. 22 and 23. The guidewire 120 andthe obturator 122 are then removed from the cannula 28.

After ensuring that all of the thumbscrews 54 and 74 are secure and thatthe alignment of the axis 170 is correct, the burring bit 150 (FIG. 23)is inserted into the cannula 28. The burring bit 150 is rotated by adrill (not shown) to burr the opposing surfaces 172 and 174 of theinferior articular process and the superior articular process on thefirst side 104 of the L4 and L5 vertebrae, respectively. Burring thesesurfaces 172 and 174 widens the facet joint 100 so that a bone graftmaterial is more easily placed into the facet joint. It is contemplatedthat the cannula 28 may be moved slightly along the facet joint 100during the burring process in order to access a larger area of the facetjoint with the burring bit 150. It should be noted that care must betaken to burr around, but not contact, the first screw 84 that waspreviously implanted across the facet joint 100 on the first side 104 ofthe vertebrae.

After the articular surfaces 172 and 174 of the facet joint 100 on thefirst side 104 of the vertebrae have been burred out around the firstscrew 84, bone graft (or bone substitute) material 160 (FIG. 24) forhelping to fuse the L4 and L5 vertebrae is placed into the facet joint100 through the cannula 28. The bone graft material 160 may be fed intothe facet joint using any known suitable instrument(s). The cannula 28is then removed from the incision on the first side 104 of the vertebraeand the first and second K-wires 12 and 14 are removed from the L5 andL4 vertebrae, respectively. The incisions are then closed. As shown inthe completed view of FIG. 24, with the two screws 84 implanted acrossthe facet joints 100 and 142 and the bone graft material 160 placed intoboth of the facet joints, fusion of the L4 and L5 vertebrae will takeplace over the next few months.

It should be understood to those skilled in the art that the apparatus10 could be used to implant screws for a variety using a transarticular(rather than translaminar) approach directly across the facet joints.Such an application could be accomplished by simply varying theplacement of the K-wires 12 and 14 to achieve the necessary screwtrajectories. It is contemplated that the implantation of transarticularscrews may be best accomplished by inserting the first K-wire 12 intothe lamina a few millimeters lateral of the spinous process rather thaninto the spinous process itself. It should be noted that the swivelblock assembly 22 could be positioned between the fixation blocks 16 and18 along the rod member 20 to aid with placement of direct (ortransarticular) facet screws.

The present invention described herein thus provides an apparatus and aminimally invasive method for placing screws either directly across thefacet joints of adjacent vertebrae or indirectly across the facet jointsthrough the lamina (i.e. translaminar) as both a primary means forspinal fixation and as a secondary means for fixation to augmentanterior fusion or pedicle screw fixation instrumentation. It iscontemplated that the apparatus could also be used to guide implantationfor a variety of other orthopedic screws in the spine as well as otherbones. Significantly, the present invention provides for the accurateand repeatable placement of facet screws and for fusing adjacentvertebrae in a minimally invasive procedure that saves time duringsurgery and is less traumatic to the patient.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. Suchimprovements, changes and modifications within the skill of the art areintended to be covered by the appended claims.

1. An apparatus for placing translaminar screws across a facet jointbetween adjacent first and second vertebrae in a minimally invasivesurgical procedure, said apparatus comprising: a first K-wire forinserting into the spinous process of the first vertebrae; a secondK-wire for inserting into a transverse process of the second vertebrae;first and second fixation blocks having perpendicularly extending firstand second passages, said first K-wire extending into said first passagein said first fixation block and said second K-wire extending into saidfirst passage in said second fixation block; a rod member extendingthrough said second passage in said first fixation block and said secondpassage in said second fixation block; a swivel block assemblycomprising relatively movable first and second block members, saidswivel block assembly including a third passage extending through saidfirst block member and a fourth passage extending through said secondblock member, said rod member extending into said third passage; and acannula which extends into said fourth passage in said second blockmember and through which the translaminar screws are insertable forimplantation across a facet joint between the first and secondvertebrae.
 2. The apparatus of claim 1 wherein said first and secondK-wires include graduations for measuring axial length along saidK-wires.
 3. The apparatus of claim 1 wherein said rod member includesgraduations for measuring axial length along said rod member.
 4. Theapparatus of claim 1 wherein said first fixation block includes a firstsecuring means for securing said first K-wire to said first fixationblock and a second securing means for securing said rod member to saidfirst fixation block.
 5. The apparatus of claim 4 wherein said secondfixation block includes a first securing means for securing said secondK-wire to said second fixation block and a second securing means forsecuring said second fixation block to said rod member.
 6. The apparatusof claim 5 wherein said first and second securing means on said firstfixation block and said first and second securing means on said secondfixation block comprise threaded fasteners.
 7. The apparatus of claim 1wherein said second fixation block includes a first securing means forsecuring said second K-wire to said second fixation block and a secondsecuring means for securing said second fixation block to said rodmember.
 8. The apparatus of claim 1 wherein said first block memberincludes securing means for securing said rod member to said first blockmember.
 9. The apparatus of claim 8 wherein said second block memberincludes securing means for securing said cannula to said second blockmember.
 10. The apparatus of claim 9 wherein said swivel block assemblyincludes securing means for securing said first and second block membersin a desired angular position relative to each other.
 11. The apparatusof claim 1 wherein said swivel block assembly includes securing meansfor securing said first and second block members in a desired angularposition relative to each other.
 12. The apparatus of claim 11 whereinsaid securing means on said first and second block members and saidswivel block assembly comprises threaded fasteners.
 13. The apparatus ofclaim 1 wherein said swivel block assembly includes positioning meansfor controllably adjusting the angular position of the first and secondblock members relative to each other.
 14. The apparatus of claim 1wherein said first and second passages in said first fixation block areoffset from each other by a predetermined amount.
 15. The apparatus ofclaim 14 wherein said first and second passages in said second fixationblock are offset from each other by said predetermined amount.
 16. Aminimally invasive apparatus for placing screws across a facet jointbetween adjacent first and second vertebrae, said apparatus comprising:a first K-wire for inserting into the spinous process of the firstvertebrae; a first fixation block removably connected to said firstK-wire; a second K-wire for inserting into a transverse process of thesecond vertebrae; a second fixation block removably connected to saidsecond K-wire; a rod member removably connected to both of said firstand second fixation blocks; a swivel block assembly comprisingrelatively movable first and second block members, said rod member beingremovably connected to said first block member; and a cannula extendingfrom said second block member and through which the screws areinsertable for implantation across the facet joint.
 17. The apparatus ofclaim 16 wherein each of said first and second K-wires includes meansfor measuring axial length along said K-wires.
 18. The apparatus ofclaim 16 wherein said rod member includes means for measuring axiallength along said rod member.
 19. The apparatus of claim 16 wherein saidswivel block assembly includes positioning means for controllablyadjusting the angular position of the first and second block membersrelative to each other.
 20. A minimally invasive surgical method forplacing screws through the lamina and across the facet joints betweenadjacent upper and lower vertebrae, said method comprising the steps of:providing an apparatus comprising first and second K-wires, first andsecond fixation blocks, a swivel block having relatively movable firstand second block members, a rod member extending between the fixationblocks and the first block member, and a cannula extending from thesecond block member; inserting the first K-wire into the center of thespinous process of the upper vertebrae; inserting the second K-wire intoa transverse process on a first side of the lower vertebrae so that thesecond K-wire is parallel to the first K-wire in both the sagittal andcoronal planes; securing the first fixation block to the first K-wirearid the second fixation block to the second K-wire with the rod memberextending across the K-wires; calculating a desired axial position forthe swivel block assembly along the rod member; calculating a desiredangle for the centerline of the cannula to extend from a second side ofthe vertebrae toward the facet joint on the first side along a firstaxis; securing the second block member of the swivel block assemblyrelative to the first block member to achieve the desired angle for thefirst axis; securing the swivel block assembly at the desired axialposition along the rod member; obtaining percutaneous access to thejunction of the lamina and the spinous process on the second side of theupper vertebrae via the cannula; inserting a first screw through thecannula; and implanting the first screw along the first axis across thefacet joint on the first side to attach the upper and lower vertebrae.21. The method of claim 20 further comprising the steps of: inserting adrill bit into the cannula prior to said step of inserting the firstscrew; and drilling a pilot hole for the first screw through the laminaand the facet joint on the first side with the drill bit to apredetermined depth along the first axis.
 22. The method of claim 20further comprising the steps of: removing the cannula from its positionover the lamina on the second side of the upper vertebrae; releasing thefirst and second block members to allow relative movement; swiveling thesecond block member to aim the centerline of the cannula along a secondaxis toward the facet joint on the second side; obtaining percutaneousaccess to the facet joint on the second side via the cannula; andplacing a bone graft material into the facet joint on the second sidethrough the cannula to assist with fusion of the upper and lowervertebrae.
 23. The method of claim 22 further comprising the steps of:inserting a burring bit into the cannula prior to said step of placing abone graft material; and burring the articular surfaces of the facetjoint on the second side to widen said facet joint for accepting thebone graft material.
 24. The method of claim 20 further comprising thesteps of: removing the cannula from percutaneous insertion on the secondside; removing the second K-wire from the transverse process on thefirst side of the lower vertebrae; inserting the second K-wire into thetransverse process on the second side of the lower vertebrae so that thesecond K-wire is parallel to the first K-wire in both the sagittal andcoronal planes; securing the second fixation block to the second K-wire;releasing the first fixation block from the first K-wire; rotating thefirst fixation block with the rod member extending across the K-wires;securing the first fixation block to the first K-wire; calculating adesired axial position for the swivel block assembly along the rodmember; calculating a desired angle for the centerline of the cannula toextend from the first side of the vertebrae toward the facet joint onthe second side along a third axis; securing the second block member ofthe swivel block assembly relative to the first block member to achievethe desired angle; securing the swivel block assembly at the desiredaxial position along the rod member; obtaining percutaneous access tothe junction of the lamina and the spinous process on the first side ofthe upper vertebrae via the cannula; inserting a second screw throughthe cannula; and implanting the second screw along the third axis acrossthe facet joint on the second side to attach the upper and lowervertebrae.
 25. The method of claim 24 further comprising the steps of:inserting a drill bit into the cannula prior to said step of insertingthe second screw; and drilling a pilot hole for the second screw throughthe lamina and the facet joint on the second side with the drill bit toa predetermined depth along the third axis.
 26. The method of claim 24further comprising the steps of: removing the cannula from its positionover the lamina on the first side of the upper vertebrae; releasing thefirst and second block members to allow relative movement; swiveling thesecond block member to aim the centerline of the cannula along a fourthaxis toward the facet joint on the first side previously secured withthe first screw; obtaining percutaneous access to the facet joint on thefirst side via the cannula; and placing a bone graft material throughthe cannula into the facet joint on the first side around the previouslyimplanted first screw to assist with fusion of the upper and lowervertebrae.
 27. The method of claim 26 further comprising the steps of:inserting a burring bit into the cannula prior to said step of placing abone graft material; and burring the articular surfaces of the facetjoint on the first side to widen said facet joint around the first screwfor accepting the bone graft material.
 28. A minimally invasive surgicalmethod for fusing adjacent upper and lower vertebrae, said methodcomprising the steps of: providing an apparatus comprising first andsecond K-wires, first and second fixation blocks, a swivel block havingrelatively movable first and second block members, a rod memberextending between the fixation blocks and the first block member, and acannula extending from the second block member; inserting the firstK-wire into the center of the spinous process of the upper vertebrae;inserting the second K-wire into the transverse process on a first sideof the lower vertebrae; securing the first fixation block to the firstK-wire and the second fixation block to the second K-wire with the rodmember extending across the K-wires; securing the second block member ofthe swivel block assembly relative to the first block member to achievea desired angle for a first axis along which a first screw will beimplanted into the facet joint on the first side; securing the swivelblock assembly at a desired axial position on the rod member; obtainingpercutaneous access along the first axis to a second side of the uppervertebrae via the cannula; inserting the first screw through thecannula; and implanting the first screw along the first axis across thefacet joint on the first side to attach the upper and lower vertebrae.29. The method of claim 28 further comprising the steps of: moving thecannula to aim the cannula toward the facet joint on the second side ofthe vertebrae along a second axis; obtaining percutaneous access alongthe second axis to the facet joint on the second side via the cannula;and placing a bone graft material into the facet joint on the secondside through the cannula to assist with fusion of the upper and lowervertebrae.
 30. The method of claim 28 further comprising the steps of:inserting a burring bit into the cannula; and burring the articularsurfaces of the facet joint on the second side to widen the said facetjoint for accepting a bone graft material.
 31. The method of claim 28further comprising the steps of: removing the cannula from percutaneousinsertion on the second side; removing the second K-wire from thetransverse process on the first side of the lower vertebrae; insertingthe second K-wire into the transverse process on the second side of thelower vertebrae; securing the second fixation block to the secondK-wire; releasing the first fixation block from the first K-wire androtating the first fixation block with the rod member extending acrossthe K-wires; securing the first fixation block to the first K-wire;securing the second block member of the swivel block assembly relativeto the first block member to achieve a desired angle for a third axis onwhich a second screw will be implanted into the facet joint on thesecond side; securing the swivel block assembly at a desired axialposition along the rod member; obtaining percutaneous access to thefirst side of the upper vertebrae via the cannula; inserting a secondscrew through the cannula; and implanting the second screw along thethird axis across the facet joint on the second side to attach the upperand lower vertebrae.
 32. The method of claim 31 further comprising thesteps of: moving the cannula to aim the cannula along a fourth axistoward the facet joint on the first side previously secured with thefirst screw; obtaining percutaneous access to the facet joint on thefirst side via the cannula; and placing a bone graft material throughthe cannula and into the facet joint on the first side around thepreviously implanted first screw to assist with fusion of the upper andlower vertebrae.
 33. The method of claim 31 further comprising the stepsof: inserting a burring bit into the cannula; and burring the articularsurfaces of the facet joint on the first side to widen said facet jointaround the first screw for accepting a bone graft material.